DefineSwitcher - switch #define in unity

DefineSwitcher.cs

using System.Collections.Generic;
using System.Linq;
using UnityEditor;
using UnityEditor.Build;
using UnityEngine;

namespace Nekomimi.Daimao
{
    /// <summary>
    /// Switch #define.
    /// rewrite <see cref="Define"/> and <seealso cref="DefineMenuPath"/>
    /// </summary>
    public class DefineSwitcher : IActiveBuildTargetChanged
    {
        #region Define

        private const string Define = "UNITY_OVR";
        private const char Separator = ';';

        private static void SetDefine(bool on)
        {
            if (on == IsDefined())
            {
                return;
            }

            var current = new HashSet<string>(CurrentDefines());

            if (on)
            {
                current.Add(Define);
            }
            else
            {
                current.Remove(Define);
            }

            PlayerSettings.SetScriptingDefineSymbolsForGroup(
                EditorUserBuildSettings.selectedBuildTargetGroup, string.Join(Separator.ToString(), current)
            );
        }

        private static IEnumerable<string> CurrentDefines()
        {
            return PlayerSettings.GetScriptingDefineSymbolsForGroup(EditorUserBuildSettings.selectedBuildTargetGroup).Split(Separator);
        }

        private static bool IsDefined()
        {
            return CurrentDefines().Contains(Define);
        }

        #endregion


        #region EditorMenu

        private const string DefineMenuPath = "Oculus/" + Define;

        [MenuItem(DefineMenuPath, priority = -1)]
        private static void SwitchDefine()
        {
            var current = IsDefined();
            SetDefine(!current);
            SetCheckState(!current);
        }

        private static void SetCheckState(bool state)
        {
            var check = Menu.GetChecked(DefineMenuPath);
            if (state == check)
            {
                return;
            }

            Menu.SetChecked(DefineMenuPath, !check);
        }

        #endregion


        #region IActiveBuildTargetChanged

        public int callbackOrder { get; } = 0;

        public void OnActiveBuildTargetChanged(BuildTarget previousTarget, BuildTarget newTarget)
        {
            SetCheckState(IsDefined());
        }

        #endregion

        #region InitializeOnLoadMethod

        private class FirstLoad : ScriptableSingleton<FirstLoad>
        {
            [SerializeField]
            public bool AlreadyLoaded = false;
        }

        [InitializeOnLoadMethod]
        private static void CheckOnLaunch()
        {
            if (FirstLoad.instance.AlreadyLoaded)
            {
                return;
            }

            FirstLoad.instance.AlreadyLoaded = true;
            SetCheckState(IsDefined());
        }

        #endregion
    }
}